Power factor correction (PFC) is used to eliminate or at least reduce harmonic currents in an input current. Harmonic currents can occur in particular in the case of nonlinear consumers, such as rectifiers with subsequent smoothing in switched mode power supplies, for example, since, in the case of such consumers, the input current is phase-shifted despite the sinusoidal input voltage and is distorted non-sinusoidally. The higher-frequency harmonics occurring in the process can be counteracted by an active or clocked power factor correction circuit connected upstream of the respective device.
Power factor correction circuits are also used in operating devices for light-emitting means, for example in electronic control gear or LED converters. The use of such circuits in devices for operating light-emitting means is desirable or necessary since standards restrict the permissible feedback of harmonics into the supply grid.
A circuit topology which is based on the topology of a boost converter is often used for power factor correction circuits. In this case, an inductance or coil to which a rectified AC voltage is supplied is charged with energy or discharged by a controllable switch being switched on and off. The discharge current of the inductance flows via a diode to an output capacitance, with the result that a DC voltage which is higher than the input voltage can be tapped off at the output. Likewise, however, other converter types are also conventional in power factor correction circuits, such as, for example, flyback converters or buck converters.
Power factor correction circuits can have a control device which controls the current consumption. For this purpose, for example, the Ton time for which the switch is switched in each case into the on state in order to store energy in the coil can be set.
Owing to undesired capacitances in the input region, it may arise that one or more of the harmonic harmonics are not suppressed to the desired extent. This can result in a current peak in the current consumption of the power factor correction circuits when the input voltage rises again.
The invention is based on the object of providing a method and a circuit for power factor correction which enable particularly effective suppression of harmonics. In particular, there is a need for such apparatuses and methods in which an undesired current peak in the case of a renewed rise in the input voltage can be reduced without changes to the capacitance in the input region, for example, being necessary for this purpose.